Alright, I found one Radioshack here in town that has most of the components and it looks like the cost can be brought down to $22 plus tax. I'd still have to order the switches and the oscillators online to save money, and I'm supposing I won't be buying wire for a while since I have three bundles of 40-50ft already. That cost is just for the parts that would be unique to each Genesis 1 HDG TMSS mod. I'm still waiting on my switches to come in, so I won't find out if it will be worth it for me to offer this mod until I'm done with my own.
What I am picturing is that the owner of the console would order or pick up all of the components and ship them with their console. I would do the work and ship it back. I generally charge $30 for repair work that takes less than four hours, which I am hoping this will be, if it takes less than one hour I'll change that. So the total cost would be ~$20-30 (discretionary) for a Model 1 HDG TMSS, ~$22 for parts and $30 for labor plus shipping.
Agostinho and I are planning on creating a tutorial for do it yourself types as well. Thoughts?